As a technique of large volume data communication, a technique in which a radio transmission apparatus spatially multiplexes and transmits a plurality of transmission data (streams) (e.g. Nmux streams, where Nmux≦Ntx) using a plurality of transmission antenna ports (e.g. Ntx antenna ports) has been studied. A radio reception apparatus spatially separates and receives received data in which the plurality of streams are mixed with each other on a propagation channel. Hereinafter, the number of streams spatially multiplexed by the radio transmission apparatus is referred to as “the number of multiplexed streams.”
When the plurality of streams are spatially multiplexed using the plurality of antenna ports, it is assumed that preamble sequences for estimating channel quality between the antenna ports of the radio transmission apparatus and the antenna ports of the radio reception apparatus are multiplexed into data signals. In this case, the radio transmission apparatus assigns different preamble sequences for each stream. The radio reception apparatus detects the preamble sequences from the antenna ports of the radio transmission apparatus, and performs channel estimation between the antenna ports of the radio transmission apparatus and the antenna ports of the radio reception apparatus.
In addition, the radio reception apparatus needs to specify the number of multiplexed streams to separate the plurality of spatially multiplexed streams. The radio reception apparatus blindly detects the preamble sequences representing the number of multiplexed streams to specify the number of multiplexed streams, which has been studied (e.g. see Patent Literature 1). Specifically, first, the radio transmission apparatus and the radio reception apparatus share candidate data of used preamble sequences. The radio transmission apparatus fixedly assigns preamble sequences to the antenna ports of the radio transmission apparatus. In the radio transmission apparatus, an antenna port to which the preamble sequence corresponding to the number of multiplexed streams can be assigned is considered as a main antenna, and the antenna ports other than the main antenna are considered as sub-antennas. For example, the radio transmission apparatus assigns the preamble sequence of a sequence number L (i.e. the largest sequence number of used preamble sequences) corresponding to the number of multiplexed streams L to the main antenna. Hereinafter, the preamble sequence corresponding to the number of multiplexed streams is referred to as “main antenna preamble sequence.”
The radio reception apparatus takes correlation between the candidate data of the preamble sequences shared with the radio transmission apparatus and the received preamble sequence, to blindly detect the preamble sequences. The radio reception apparatus specifies the preamble sequence of the largest sequence number from the blindly detected preamble sequences, as the main antenna preamble sequence, and the specified preamble sequence number L is referred to as the number of multiplexed streams. The radio reception apparatus estimates channel quality using the detected preamble sequence, and performs spatiotemporal decoding on the basis of the number of multiplexed streams L.